The Australian Transport Safety Bureau (ATSB) is Australia's national transport safety investigator. The ATSB's function is to improve safety and public confidence in the aviation, marine and rail modes of transport. The ATSB is Australia's prime agency for the independent investigation of civil aviation, rail and maritime accidents, incidents and safety deficiencies.

Aviation safety investigations & reports

Eurocopter International Pacific Limited EC120B, VH-ADC

At 1110 Eastern Standard Time on 12 May 2005, a Eurocopter
EC120B helicopter, registered VH-ADC, departed Canberra enroute to
Jindabyne, NSW, with the pilot and two passengers on board. The
pilot reported that at about 30 minutes after departure, while in
cruise flight at 5,000 ft above ground level in smooth flying
conditions, the main rotor speed (NR) RPM audio warning
sounded.

The pilot reported that a scan of the instrument panel revealed
that the NR was exceeding 450 RPM and that he then used the
collective pitch lever to reduce the NR. The pilot noted that it
took approximately 5 to 7 seconds to arrest the high NR rate, which
then silenced the audio warning. The helicopter was flared for
landing as it lost altitude and impacted the undulating ground It
then bounced back into the air momentarily, before it impacted the
ground once more and slid to a halt. The pilot then applied the
rotor brake to stop main rotor rotation and assisted the passengers
to exit the helicopter. There were no injuries to the passengers
and minor injuries to the pilot.

The helicopter was determined to be within weight and balance
limitations and carried sufficient fuel for the flight. Testing of
the engine could not duplicate the in-flight engine shutdown as
reported.

At 1110 Eastern Standard Time on 12 May 2005, a Eurocopter
EC120B helicopter, registered VH-ADC, departed Canberra for
Jindabyne, NSW, with the pilot and two passengers. The pilot
reported that about 30 minutes after departure, while in cruise
flight at 5,000 ft above mean sea level (AMSL) in smooth flying
conditions, the main rotor speed (NR) RPM audio warning
sounded1. The pilot reported that a
scan of the instrument panel revealed that the NR was exceeding 450
RPM and that he then lowered the collective pitch lever. He
reported that after entering an autorotation configuration, it took
approximately 5 to 7 seconds to arrest the high NR rate by lifting
the collective lever, which then reduce the NR and silenced the
audio warning2.

The pilot further reported that he completed a left turn towards
a cleared area and lined the helicopter up on a north-easterly
heading, while rapidly losing altitude before turning towards the
south-east over trees to the clearing. The pilot flared the
helicopter for landing, but noted no perception of power from the
engine (audible or torque) and the helicopter sank through the
flare before it impacted the undulating ground. It then bounced
back into the air momentarily, before it impacted the ground once
more and slid to a halt. The pilot then applied the rotor brake to
stop main rotor rotation and assisted the passengers to exit the
helicopter. There were no injuries to the passengers and only minor
injuries to the pilot. The elevation at the final resting place of
the helicopter was about 4,340 ft AMSL.

The helicopter was determined to be within weight and balance
limits and carried sufficient fuel for the flight.

The helicopter sustained damage to the main rotor blade tip
caps, front skid landing gear, front bottom canopy and aft upper
tail cone/fenstron area. During the landing sequence, the main
rotor blades had contacted the aft upper tail cone/fenstron area as
a result of the flaring of the helicopter. The initial impact
ground scars of the helicopter skid landing gear were reported to
have been about 35 m from the final resting place of the
wreckage.

At the time of the occurrence, the helicopter had accumulated
195.9 hours total airframe time. The Turbomeca model Arrius 2F
engine, serial number 34039, had been installed on 28 February 2005
with 736.8 hours time since new. At the time of the accident, the
engine had accumulated 775.0 hours time since new. The engine was a
replacement engine that had been provided by the engine
manufacturer while the original engine was being repaired.

The original engine had been removed for an unrelated
over-torque event. An examination the helicopter's operational and
maintenance records conducted by the Civil Aviation Safety
Authority (CASA) found that the helicopter had been maintained
correctly and satisfactory records maintained.

Following the accident, the engine was removed and shipped to
the engine manufacturer for testing, disassembly and examination
under the supervision of the Bureau d' Enquetes et d' Analyses of
France, on behalf of the Australian Transport Safety Bureau. The
engine was placed into a test cell and operated to confirm
operating parameters. The engine was tested through all operating
parameters without any abnormal vibrations, high temperatures,
overspeeding or other anomalies. The fuel control unit was then
removed and bench tested with no anomalies found. Testing,
disassembly and examination of the engine did not reveal any
anomalies that could have contributed to the in-flight shutdown as
reported.

The helicopter's on-board diagnostic equipment was accessed
immediately following the event. The maintenance page of the
equipment displayed only a fault code indicating that an over limit
NR event to 462 RPM had taken place. No other faults were
displayed.

The rotorcraft flight manual included a section entitled ENGINE
FLAME-OUT, which detailed procedures in the event of an engine
flame-out in cruise flight including:

AUTOROTATION PROCEDURES OVERLAND

Collective pitch…………REDUCE to maintain NR in green arc.

The rotorcraft flight manual also included a section entitled
ENGINE GOVERNOR FAILURE which detailed emergency procedures for a
rapid increase in NR as follows:

NR INCREASE

Simultaneously to maintain NR in green arc:

Collective……………….INCREASE

Twist Grip………………SLIGHTLY REDUCE

NOTE
During the flight, the pilot shall control NR using the twist
grip.

The rotorcraft flight manual did not include procedures
specifically related to a sudden increase in NR during cruise
flight. However, the CASA requirements for the granting of a
helicopter licence require a pilot to demonstrate the ability to
control NR within rotorcraft flight manual limits. During this
training, pilots are taught to control the NR utilising both the
collective lever and the throttle twist grip.

An intermittent tone activated at
420 RPM NR. Normal operating range for NR was 390 to 415 RPM, the
caution range was 415 to 447 RPM with 447 RPM the maximum with
power off.

Increasing collective pitch of the
main rotor blades using the collective pitch lever reduces the NR
by slowing down the rotational speed of the blades for that given
engine power setting.

The nature of the terrain in the vicinity of the accident site
was such that potential emergency landing areas were limited and
added to the complexity of the task of the pilot in responding to
the in-flight emergency. The factors surrounding the in-flight
shutdown of the engine could not be determined, as the problem
could not be replicated in the engine test cell. No engine shutdown
was recorded on the on-board diagnostic equipment.

The rotorcraft flight manual contained no specific information
on an event such as that reported. However, the pilot's reaction to
the main rotor RPM audio warning appeared inconsistent with the
only guidance provided in the rotorcraft flight manual relating to
an increase in main rotor RPM.